Fibre conduit



Nov. 22,

Filed Oct.

R. EWING ET AL FIBRE CONDUIT 2 Sheets-Sheet l INVENTORS Rei d E w1;711,5

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NOV- 22, 1955 R. EwlNG ETAL 2,724,189

FIBRE CONDUIT Filed Oct. 1l, 1951 2 Sheets-Sheet 2 INVENTORS ReidE'w111g Reid Ewing United States Patent O FIBRE `CONDUI'I and LloydEwing, Milwaukee, Wis., assignor to McGraw Electric Company, Milwaukee,Wis., a corporation of Delaware Application October 11, 1951, Serial No.250,926 6 Claims. (Cl. 34-7) This invention relates to an improvement inthe method of drying and producing fibre conduit which are` formed ofwoundpaper pulp or other brous material.

Fibre conduit impregnated with pitch has been found to be an excellentencasing means for electric cables because it can be imbedded in theground or in concrete. The pitch prevents roots from penetrating it; itslight weight makes it easy to transport and install and the cost is low.However, there has been one flaw in thisotherwise lsatisfactory pipingmeans. `It is the problem of delamination, which is a splitting apart oflayers within the conduit. This causes weakness in the conduit structureand often unevenness on the inner surface of the same. Delamination is acondition that is apt to grow worse. Being a weak spot, the weakness isincreased when covered with wet concrete and during curing of the sameto the extent that the layers of the conduit may fray and catch on thecables that are subsequently pulled through it. Each time a cable isreplaced or new cable added and pulled through the conduit, the looselayers catch and rip farther until that section of conduit becomes fullof obstruction `and has to be replaced with the attendant expense andlabor, as the breaking up and removal of concrete is not easily done.

It `can readily be seen why so many efforts have been made to solve thisproblem of delamination. E. G. Henslcr, in his patent entitled Method ofMaking Paper Tubes, No. 2,532,494 and assigned to the assignee of thisinvention, thought that he had solved the problem by adding a narrow brestrip at the end of the tube and` then drying by directing warm airblasts at the end of the added fibre strip and through the mandrel. Thismethod has not eliminated the problem of delamination. Others,` also,have worked on the problem without much success.

It was not until our inventive ideas were used that this problem wasfinally solved. i i

Aprincipal object of this invention is to provide a means for drying thefibre tube by withdrawing the moisture uniformly through the outerperipheral wall only.

Another object is to provide a means of eliminating heat transfer on theinside of the tube during drying.

Still another object is to provide a means of cooling the inner surfaceof the tube during drying.

A further object is to provide a means of drying fibrous material fromone surface in such a manner that air pockets will not occur.

Also, an object is to providea means whereby the end of the fibre tubewill dry at the same rate as the interior section.

Another object of this invention is to provide a means of drying fibretube whereby the shrinkage involved in the drying process takes place insuch a manner that the fibre tube becomes a uniformly integrated solidtube.`

Various methods of achieving these objectives are shown in theaccompanying drawings in which:

Fig. 1 is a fragmentary horizontal sectional view of the "ice 2 fibretube on a sleeve with an insulating block enveloping the end of thesleeve and the end of the fibre tube.

Fig. 2 is a fragmentary horizontal sectional View of the fibre tubing ona composite sleeve consisting of an insulating material forming the endsof the sleeve.

Fig. 3 is a fragmentary horizontal sectional view of the fibre tubingwithout a sleeve but with an insulating plug at the end.

Fig. 4 is a fragmentary horizontal sectional view of the fibre tube on asleeve, the bre tube having tapered ends.

Fig. 5 is a fragmentary horizontal sectional View with the fibre tubingon a sleeve with a cooling means applied to the sleeve.

Fig. 6 is a fragmentary horizontal sectional view of a fibre tubingwound around a sleeve that is made of insulating material.

Fig. 7 is an enlarged fragmentary horizontal sectional view of the fibretubing dried by the method shown in Figs. l and 2.

Fig. 8 is an enlarged fragmentary horizontal sectional view of the fibretubing showing a void created by unsuccessful drying.

Fig. 9 is a fragmentary horizontal sectional View of the fibre tubing ofFigs. 5 and 6 showing their shape after drying.

Like numerals represent like parts in the following specication. t

With this method of making fibre tubing the fibre pulp is wound on asleeve which fits over a mandrel during the winding and when winding hasbeen completed the sleeve with its layers of wound fibre tubing isremoved from the mandrel for the drying process.

In Fig. 8, we show the problem that we are trying to overcome.` A wetfibre tube 1 ona sleeve 2 is dried by the process of evaporating themoisture out of the fibre duction to the inner surface of the fibretube. Evaporation `cannot takeplace on the inner surface because of thesleeve but the heat conducted by the sleeve 2 forces the moisture awayfrom the sleeve outwardly until it escapes throughthe outer surface 3.While evaporation is taking place, shrinkage is` also taking place untilthe point is reached where there is no more moisture in a section of thefibre tubing and shrinkage ceases. That section is set and forms aporous unyielding crust through which the further evaporation of the wetinner section between the surfaces takes place. The evaporation of thisinner section and subsequent shrinkage tends to form dry layers whichbow toward both dry surfaces as shown at 5. This shrinkage within theset outer crust creates voids 6 in the fibre tubing. These voids 6 areweak spots and cause delaminations, cracking and breaking. This, ofcourse, is a serious danger that must be avoided.

Tests have shown that moisture can travel along the unbroken sheetconsiderably faster than it can travel from sheet to sheet where thepoints of fire contact are much fewer. The factors that control theserelative rates of moisture removal apparently are the factors thatgovern the tendency to split. This theory corresponds with the knownfacts that higher drying temperatures and thicker tubes exhibited anincreased tendency to split.

When the tubes are dried on sleeves the splits occur at the ends of thetubes, seldom extending more than six inches inward from the end andvery rarely extending all the way to the other end of the tube. The useof sleeves has been a tremendous help, as the drying time without 3sleeves takes as long as three to five days, with splits sometimesextending most of the tube length. The tubes on the sleeves are placedin drying rooms and air, heated to 145 is brown through. This processtakes about 18 hours.

We have found that by thermally insulating the sleeve y ends or bythermally enclosing the sleeve ends and ends of the fibre tubes,splitting can be eliminated.

We show five methods of achieving this, and illustrate them more or lesssymbolically, especialy, the layers of fibrous pulp which may beconsiderably more in number.

In Fig. l we show a sleeve 7 surrounded by a fibre tubing 8 and aninsulating block 9. This insulating block 9 has an opening 10 and adiagonally shaped lip 11. The end of the sleeve 7 is injected into theopening 10 of the insulating block 9 until the end 3a of the fibretubing 8 is wedged against the diagonal lip 11. In this manner, theinsulating block 9 prevents the end of the tube from drying faster thanthe middle of the tube and also prevents heat from being conducted downthe sleeve to the inner surface of the fibre tube.

A variation of the same principle is illustrated in Fig. 2 Vin which asleeve 12 is composed of insulating ends 13 integral with the bodysection 14 which may be made of some conductive material such asaluminum. Fibre tubing 15' is wound around this sleeve 12, and theinsulating ends 13, possibly made of some plastic material, preventdrying at the ends or from the inside to take place faster than in therest of the tubing.

Fig. 3 illustrates a way of attaining uniform drying of a fibre tube 16without a sleeve, by using insulating end plugs 17 at both ends thatextend somewhat into the inner opening 1S of the fibre tube'16 and alsoextends like a cap across the end of the fibre 'tubes at 17a. Thisinsulating plug aids in uniform drying because it prevents evaporationat the end of thefibre tube and reduces heat transfer to the innersurface of the fibre tube. This method is used on tubes of heavier wallthickness.

Another method of reducing splitting at the ends of the fibre tubing isshown in Fig. 4. Sleeve 19 has a fibre tube 20 wrapped around it. Thefibre tube 20 has tapered ends 21. This taper, by making the tubethinner near the end, helps to prevent splitting in the tube such as isillustrated in Fig. 8.

The methods illustrated in Figs. 3 and 4 are an improvement over presentmethods in the'prevention of splitting and air pockets but are not aseffective as the methods shown in Figs. 1 and 2.

In Fig. 5 another form is shown. Heat transfer along the mandrel isretarded by cooling the sleeve 22 with some cooling means 23 such as anair spray or an atomized water spray from a tube 24. The cooling of thesleeve 2?. reduces heat transfer along the sleeve and aids in forcingall evaporation to take place from the outer surface of the fibre tube25.

Fig. 6 illustrats a sleeve 26 made of some insulating material. Thisprevents'heat transfer to the inner surface of the fibre tube 27, thusdirecting all evaporation to take place off the outer surface.

The desired result of our method is shown in Figs. 7 and 9. Fig. 7illustrates the shape taken by the fibre tubes of Figs. 1 and 2. Afragment of a fibre tube 30 is shown on a fragment of a mandrel 31. Aswet tubing it occupies the space from the circumference 32 of the sleeve31 to the outer line 33. As evaporation takes place along the outer edge33, shrinkage takes place. When all the moisture is evaporated out ofaportion of the fibre, shrinkage ceases and that portion becomes hardand set. The line 35 within the original outer surface 33 of the tube 30represents the new outer line after shrinkage.

The inner part of the fibre tube is still wet so evaporation mustcontinue through the pores in the outer crust along the line 35. Sinceheat does not travel along the sleeve because of insulating ends 37, itis not conveyed or conducted' to the inner surface. Any drying means,l

. but as it occurs from the outer edge the next section to dry is thesection adjacent the outer crust thus as it shrinks it shrinks towardthe hard outer ring. This continues until the entire tube is devoid ofmoisture and shrunk to its ultimate extent, each layer adhering toanother outer pre-dried, pre-shrunk layer. This inside diameter 38 willthen be greater than when the fibre was wound around the sleeve and thefibre tubing will be one strong porous piece without dangerous voids anddelaminations. A satisfactory tube is the result.

Fig. 9 illustrates the shape taken by the fibre tubes of Figs. 5 and 6when they dry. The sleeve is insulated but not the ends of the fibretubes, consequently evaporation and subsequent shrinkage takes place offthe end surface 40 as well as the side surface 41. When the surfaces it?and 41 are dry, they will have shrunk to the lines 42 and 43 andtheinner surface, of the tube will have shrunk from the outer diameter ofthe sleeve 44 to the larger I. D. 45. Since the evaporation takes placetoward the outer surfaces 40 and 41, the ends do not shrink away fromthe sleeve but instead dry to the shape Villustrated with a smaller I.D. on the inner side of the end at 46. This smaller I. D. 46 is removedduring the machining process so that the entire inner surface becomes auniformly larger diameter than the outer diameter of the mandrel.

We claim:

' 1. A method of drying a moist fibre conduit formed of a plurality ofwound paper pulp layers comprising the steps of providing an insulatingbarrier means adjacent to at least one end thereof, applying a tiuiddrying medium solely to the exterior surface of said conduit, andcontinuing the drying process to remove moisture therefrom in adirection towards the outer surface only and until the conduit isthoroughly dry and set.

2. A method of drying a moist fibre conduit formed of a plurality ofwound paper pulp layers on a sleeve cornprising the steps of sealing anend of said sleeve and providing an insulating barrier meansvimmediately contiguous the adjacent end of the conduit, applying adrying fluid of low moisture content solely to the exterior surface ofsaid conduit, and continuing the drying process to remove moisturetherefrom in a direction towards the outer surface only and until theconduit is thoroughly dry and set.

' 3. A method of drying a moist fibre conduit formed of a plurality ofwound paper pulp layers on a sleeve comprising the steps of providing aninsulating barrier plug for an end of said eleeve and adjacent to thecorresponding end of said conduit, applying a heated uid of low moisturecontent solely to the exterior surface of said conduit, and continuingthe drying process to remove moisturetherefrom in a direction towardsthe outer surface only and until the conduit is thoroughly dry and set.

4.- Av method of drying a moist tubular fibrous article on a sleeveprojecting axially therefrom, comprising the steps of directing a 'heatinsulating and cooling fiuid towards the extending portion of saidsleeve, applying a uid drying medium solely to the exterior surface ofsaid tubular article, and continuing the drying process to removemoisture therefrom in a direction towards the outer surface only anduntil the article is thoroughly dry and set.

5. A method of drying a moist fiber conduit formed of a plurality ofwound paper pulp layers which has previously been formed on a thermallyinsulating sleeve, and comprising the steps of providing an insulatingbarrier means immediately contiguous at least one end of the sleeve andadjacent end of the conduit, applying a heated fluid drying agent solelytothe exterior surface of said conduit, and continuing the dryingprocess to remove moisture. therefrom in a direction towards the outersurface only and until the conduit is thoroughly dry and set.

6, A method of drying a moist ber conduitformed of a plurality of woundpaper pulp layers having tapered ends comprising the steps of providingan insulating barrier means immediately contiguous the tapered ends ofthe conduit, applying a heated uid drying agent solely to the exteriorsurface of said conduit, and continuing the drying process to removemoisture therefrom in a direction towards the outer surface only anduntil the conduit is thoroughly dry and set.

References Cited in the file of this patent UNITED STATES PATENTSLaraway Mar. 30, 1886 Lewis et al June 28, 1938 Jones Dec. 26, 1939Mengeringhausen et al. Dec. 16, 1941 Fryer et al. June 8, 1943 NebesarMar. 22, 1949 Hensler Dec. 5, 1950

